The known telescopic extensions for electric household appliances comprise an inner tube and an outer tube sealingly slidable one inside the other, a sleeve, a fastening means adapted to lock together the inner tube and outer tube, a thrusting slider engaging with the fastening means via the action of resilient means and actuating means operationally connected to the thrusting slider. In these extensions, the inner tube is provided with a row of notches of predefined shape and the sleeve is fixed to the outer tube.
Telescopic extensions of the abovementioned type are known, for example, from EP 1 092 383 A1, EP 0 520 534 B1, EP 0 987 976 B1 and EP 01993418.1, all in the name of the same Applicant. The telescopic extensions mentioned above are all very efficient and practical to use.
Other telescopic extensions are known from EP 0 552 481 B1, EP 0 553 482 A1 and DE 196 15 814 A1.
In particular, EP 0 552 481 describes a telescopic tube for electric household appliances with an inner tube and outer tube slidable one inside the other; a sleeve fixed to the outer tube; and a fastening means able to lock together the inner tube and the outer tube. An actuating pushbutton consisting of two pieces retained in a central position by two springs is provided in the telescopic tube according to EP 0 552 48. The bottom piece of the actuating pushbutton has outwardly projecting parts which are engaged via a cavity in the top part of the two-piece pushbutton. The sleeve is housed inside a cavity formed by flaring the outer tube in the vicinity of its end.
The telescopic tube for an electric household appliance according to EP 0 552 481 has various drawbacks. The flaring is a costly operation which increases greatly the cross section of the telescopic tube. Moreover, it greatly stresses the metallic walls of the tube, weakens them and very often causes damage which results in rejection of the finished part. This results in high production costs. In order to prevent the outer tube from rotating with respect to the inner tube, a longitudinal relief must be necessarily provided in the inner tube and a corresponding longitudinal recess provided in the outer tube.
The telescopic tube for an electric household appliance according to EP 0 552 481 is difficult to assemble owing to the outwardly projecting parts of the bottom piece of the actuating pushbutton. In fact, the bottom part of the pushbutton cannot be mounted by inserting the sleeve in the outer tube. The bottom part of the pushbutton must be mounted from above and this operation is difficult owing to the presence of the two springs. Assembly therefore cannot be automated.
The telescopic tube for an electric household appliance according to EP 0 552 481 is not considered safe owing to the fact that the top part of the pushbutton may be separated from the bottom part and the entire device may therefore break and become unusable.
The Applicant, in particular, has perceived the need to reduce the number of components which form the mechanism and provide a mechanism which is easy to assemble.
The Applicant has also perceived the need to provide a telescopic extension which is strong and entirely reliable in any operating condition.
According to the technology disclosed herein a telescopic extension for an electric household appliance is provided, said extension comprising: an inner tube and an outer tube which are slidable one inside the other; a sleeve fixed to the outer tube; a fastening means adapted to lock together the inner tube and the outer tube; a slider co-operating with the fastening means via the action of a first spring-land a second spring; and an actuating handle operationally connected to said slider. The inner tube is provided with a plurality of recesses able to receive, at least partially, the fastening means. The outer tube comprises a tunnel for retaining the slider and for guiding it during displacement; the tunnel is formed by suitably shaping the outer tube. The sleeve comprises a recessed area for retaining the slider and guiding it during displacement. The inner tube has a depression forming a channel which extends longitudinally. Recesses for the fastening means are provided on the bottom of the channel.
Conveniently, the tunnel has two sides walls and a ceiling which connects together the two side walls.
In an advantageous embodiment, the tunnel comprises at least two windows formed in the ceiling of the tunnel, the two windows defining between them a central connecting strip which connects the two side walls of the tunnel.
Conveniently, the surface of the slider is in contact, at least partially, with the central connecting strip in any operating condition of the slider. The surface of the slider which is in contact, at least partially, with the central connecting strip is flat and does not have parts projecting from the ceiling of the tunnel.
Preferably the actuating handle comprises a longitudinal recess for receiving the tunnel of the outer tube. The actuating handle comprises two teeth projecting from the bottom of the longitudinal recess, the distance between the two teeth corresponding to the length of the slider.
The end surface of the teeth conveniently has a rounded form for retaining the springs.
The slider conveniently comprises two side holes for receiving a respective end of the two springs.
The actuating handle preferably consists of two pieces and comprises means for locking together the two pieces.
According to a second aspect, the technology disclosed herein relates to an electric household appliance comprising a telescopic extension as mentioned above.
The telescopic extension of the technology disclosed herein has the advantage of being extremely compact and particularly resistant to the operating stresses such as axial thrusts, transverse thrusts and twisting moments.
Moreover, it may be assembled using a significantly simplified process which allows a reduction in the time and production costs and may be easily automated.